Generally, it has been known to provide a cab on a construction machine like a hydraulic excavator. A cab on a construction machine of this sort is often fitted with a door to be opened and closed by an operator (e.g., as disclosed in Patent Literatures 1, 2 and 3 below).    Patent Literature 1: Japanese Patent Laid-Open No. H1-198929    Patent Literature 2: WO99/61711    Patent Literature 3: Japanese Patent Laid-Open No. H11-100864
Prior art hydraulic excavators of this sort are largely constituted by a vehicular lower structure and an upper revolving structure which is rotatably mounted on the vehicular lower structure, and a cab is usually built on a revolving frame of the upper revolving structure. Normally, the cab is in the form of a hollow box-like structure, i.e., the so-called “a cab box” which is constituted by five pillars which are erected in left front, right front, left center, left rear and right rear positions, and five side sections between the five pillars, including front, left front, left rear, right, and rear side sections. A door is openably or closeably fitted between the left front and left center pillars of the cab box.
In the case of prior art cabs which are disclosed in Patent Literatures 1 and 2 mentioned above, a door is formed by a single door panel of a flat plate-like shape, and pivotally hinged to the left center pillar of the cab box in such a way that it can be swung open outward of the cab box.
Further, in the case of Patent Literature 3 mentioned above, a cab is provided with a folding type door having a couple of door panels which are pivotally connected to each other. More specifically, this folding type door is constituted by a first door panel which is pivotally attached to a left center pillar, and a second door panel which is pivotally connected to a front side of the first door panel. When the folding type door is largely opened, a striker which is provided on the outer side of the second door panel is attachably or detachably engaged with a catch which is provided on a left rear section of the cab box. Thus, when it is desired to leave the folding type door in an opened state during an operation of the machine, it can be locked in an open position by opening the door until the striker comes into engagement with the catch on the side of the cab box.
Further, in the case of this prior art folding type door, when the folding type door is closed, the two door panels are retained in a slightly bent form, and a part of a revolving frame under the door is projected sideward of the closed door.
In the case of the prior art cabs in Patent Literatures 1 and 2, a cab door is constituted by a single door panel which can be swung open toward outside. In this connection, considering the possibilities that a cab door is left open during certain machine operations, it is desirable to minimize sideward outrunning of an opened door beyond the width of a vehicle body at the time of laying out or designing the vehicle body, ensuring that an opened door will not obstruct machine operations.
In this regard, it is conceivable to relocate the cab as a whole to the center of a vehicle body. However, considering positional relations with the cab and other structures, the relocation of the cab is feasible only in a limited range which would not be effective for minimizing a sideward outrunning of an opened cab door to a sufficient degree.
Therefore, in the case of the cabs in Patent Literatures 1 and 2, in order to minimize a sideward outrunning of an opened cab door, it becomes necessary to cut the dimensions of a cab itself. In such a case, it becomes difficult to secure a sufficient space within the cab, resulting in deteriorations in operating environment.
Further, in the case of the prior art described in Patent Literature 3, of the two door panels which make up a folding type door, a striker is provided on the second door panel alone and, when the door is opened, brought into engagement with a catch which is provided on the part of a cab box. The first door panel is not fixed to the side of the cab box, so that it is put in rattling or vibratory movements and considerably deteriorated in durability, due to plays in hinges which rotatably support the first door panel.
Furthermore, in the case of the prior art described in Patent Literature 3, a side panel at the outer periphery of a revolving frame is projected beyond an outer side surface of the cab, providing a space for receiving a folded door which is opened state. Therefore, when the machine is used at a working site in a cold district or in winter, snow falls on the projected part of the revolving frame while the machine is operated or parked on a snowing site, to make it difficult to open the door, as a result degrading efficiency of operation. Besides, at the time of a ground excavating operation, soil tend to deposit and accumulate on the projected part of the revolving frame.